This invention relates to an improved biodegradable dye penetrant composition and method for non-destructively testing material specimens to locate and identify surface voids, cracks or defects, and is particularly concerned with the provision of an improved water washable biodegradable dye penetrant composition or solution containing a specific relatively non-volatile solvent for thinning such water washable dye penetrant, such solvent being preferentially removable from the part surface followed by removal of excess dye penetrant, upon application of water to an object to which the dye penetrant composition has been applied, the dye penetrant composition remaining in the cracks and voids of the part having substantially the same properties as the initial composition in the absence of such solvent, particularly substantially the same sensitivity, the biodegradability of the excess dye penetrant removed from the object surface being substantially unaffected by such solvent. The invention is also concerned with the method of employing such thinned water washable dye penetrant composition in a penetrant inspection process.
In known penetrant inspection methods for rapid location and evaluation of surface flaws or cracks in test bodies or parts, a dye penetrant composition, preferably containing a fluorescent dye, and which will penetrate the openings of the surface cracks or flaws in the part, is applied to the surface of the test body, and the excess penetrant composition is removed from the surface of the body. A developer composition may then be applied to the part surface, which acts as a wick and causes the liquid penetrant containing the fluorescent dye, which was retained in the cracks or surface flaws, to be drawn up out of the surface defects by capillary action. The part is then exposed to appropriate lighting conditions, such as invisible fluorescigenous light, and the location of the surface flaws is revealed by the emission of visible fluorescent light by the penetrant dye which was retained in the cracks or flaws after the penetrant composition was removed from the surface of the part.
For best efficiency, particularly for the detection and location of minute surface cracks and flaws, as well as intermediate size and gross cracks, it is necessary that the dye penetrant composition have high sensitivity.
Volatile type solvents are commonly employed for extending or thinning dye penetrant inspection solutions or compositions. This is done chiefly for the purpose of lowering the viscosity of the penetrant in order to adapt it for application in spraying systems. Thus for example solvents such as kerosene, light fuel oils, and methyl ethyl ketone, all highly volatile solvents, have heretofore been employed in prior art dye penetrants. See for example U.S. Pat. No. 2,806,959.
Another reason for thinning a penetrant solution is the resulting economy due to the extending effect which the solvent has in the penetrant solution. However, for this purpose, the solvent must evaporate quickly after its application to a part surface, otherwise the properties of the penetrant, such as fluorescence and sensitivity are greatly reduced by the presence of a solvent which does not evaporate. Therefore, the use of volatile solvents has heretofore generally been considered necessary for this purpose.
However, the use of volatile solvents in dye penetrant compositions has certain disadvantages. Thus, the use of volatile solvents in dye penetrants results in the evolution of fumes and solvent vapors which are rapidly formed by the evaporating solvent.
An additional criterion has recently developed also with respect to dye penetrant solutions and compositions. Generally, dye penetrant solutions presently being used and containing solvents and wetting agents present a disposal problem in that they are substantially non-biodegradable, that is, they are very difficult to decompose by bacteria in sewage disposal plants. Hence the necessity for the development of dye penetrant solutions and compositions which are biodegradable, that is which employ dye solvents and carriers which are biodegradable, and are readily available despite the petrochemical shortage, has attained considerable importance.
In my above copending applications there is disclosed a novel dye penetrant which has improved washability and sensitivity characteristics, and which is biodegradable, containing as the vehicle for the dye, certain biodegradable nonionic ethoxylated alcohols, or combinations thereof.
In my U.S. Pat. No. 3,777,157 there is disclosed a water washable dye penetrant composition which comprises N-methyl-2-pyrrolidone, a mixture of a ketone and wetting agents, a fluorescent dye and glycol monobutyl ether which functions as a thinner for the dye penetrant composition. Although such dye penetrant composition has been found effective, it has the disadvantages of requiring a multiplicity of dye carriers or solvents, with proper balance thereof necessary to provide a desired sensitivity, and the composition is not biodegradable.
Accordingly, the main object of the present invention is the provision of a water washable biodegradable dye penetrant solution or composition which avoids the use of volatile solvents and its above noted disadvantages, yet which can be readily applied as by spraying to a part surface and readily removed following application of the dye penetrant to a test body, substantially without affecting the properties of the dye penetrant composition, and particularly its sensitivity and biodegradability. An additional object is the provision of procedure for utilizing such improved water washable dye penetrant composition in a dye penetrant inspection method.